A clutch assembly of this type is the subject matter of commonly owned U.S. Pat. No. 4,349,090, in the name of one of us, Walter Griesser, and application Ser. No. 312,129 filed Oct. 16, 1981 now U.S. Pat. No. 4,425,990 by the same applicant. According to these prior disclosures, an externally toothed first (e.g. driving) gear carries several peripherally spaced spring-loaded detent members or rockers which extend radially into an inner peripheral groove of the internally toothed coupling sleeve while the latter is in a decoupling position, i.e. is disengaged from a coaxially adjoining second (e.g. driven) gear having external teeth of the same diameter and pitch. Upon an incipient coupling shift of the sleeve, i.e. an axial displacement thereof toward the second gear, the rockers exert an axial thrust upon a synchro ring which is limitedly rotatable relatively to the first gear and has a clutch surface confronting a similar surface of the second gear across a narrow clearance. As that clearance is eliminated by the thrust, the synchro ring is frictionally coupled with the second gear and is limitedly rotated, relatively to the first gear, about the common gear axis. This relative rotation, in a direction dependent on the speed difference between the two gears, causes each rocker to come to rest against one of two bracketing projections on the synchro ring so as to prevent a radial inward displacement of the rockers by camming engagement with the sleeve until the speed difference between the two gears has been substantially eliminated. It is only then that the sleeve can cam the rockers radially inward to complete the coupling shift.
The rocker members of the described clutch assembly act as levers whose mechanical advantage amplifies the exerted gear-shifting force as transmitted to the coacting clutch surfaces of the synchro ring and the second gear. This mechanical advantage enables a significant acceleration of the coupling shift since the time t for completing that shift is given by ##EQU1## where J is the mass moment of inertia of the rotating parts whose speed is to be changed, .DELTA..omega. represents the difference in the rotary speeds of the two gears and k is a proportionality factor. The effective increase in the exerted axial force F.sub.a is particularly useful for the shifting of gears in heavy-duty vehicles, such as trucks or tractors, which in many instances are still being shifted manually.
Certain shortcomings of that prior clutch assembly, however, call for further improvement. Thus, the axial thrust exerted upon the synchro ring in the initial phase of a coupling shift is transmitted via beveled surfaces of the sleeve and the rockers giving rise to additional resistance components that must be overcome. The frictional resistance increases with the leverage and may cause jamming even with relatively small values of the aforementioned mechanical advantage. The completion of the shift requires a radially inward depression of the rockers against the force of their biasing springs which is supplemented by the centrifugal force of the rotatin first gear. Moreover, if the confronting clutch surfaces of the synchro ring and the second gear are frustoconical (they could also be formed by interleaved annular friction disks as likewise disclosed in the two prior applications), the combined radial and pivotal motion of the rockers may tend to disalign the two clutch surfaces so as to cause unsymmetrical wear.
In another commonly owned pending application, Ser. No. 391,868, filed June 24, 1982 by Erich Tausend now U.S. Pat. No. 4,475,639, there has been disclosed a modified clutch assembly designed to obviate some of the drawbacks of earlier systems. According to that disclosure, the inner peripheral groove of the coupling sleeve is replaced by an axially disposed inner guide groove associated with each detent member or rocker, the latter being universally jointed to the aforementioned first gear at a fixed fulcrum. In the decoupling position, in which the inner teeth of the sleeve are not in mesh with the outer teeth of a coaxially adjoining second gear, a free end of each rocker extends radially into the respective guide groove which has lateral pockets positioned to receive that free end and limit its motion in an axial plane upon a relative angular disalignment of the synchro ring and the first gear from a normal median position thereof; such angular disalignment results from a speed difference between the first and second gears upon the establishment of frictional contact between the clutch surfaces of the second gear and the synchro ring by an axial thrust exerted at the beginning of a coupling shift upon the latter through the intermediary of the rockers. The lateral pockets of each guide groove are bounded by camming edges dislodging the free end of the associated rocker therefrom in response to a continuing axial thrust, upon establishment of substantial synchronism between the two gears, to enable a completion of the coupling shift.
As further disclosed in the Tausend application, the free end of each rocker is provided with a spring-loaded contact element--specifically a sphere--receivable in a central depression of the bottom of the respective guide groove when the sleeve is in its decoupling position. That application also teaches the formation of each guide groove in a separate insert which, after machining, is fitted into the sleeve.
Another peculiarity of the assembly disclosed in the Tausend application is the fact that each rocker, which is prevented from moving radially on account of its fixed fulcrum, bears a collar that is limited tiltable as well as radially slidable thereon and is spring-biased in a radially outward direction against overhanging shoulders of the synchro ring in order to center same on the gear axis. The interposition of such a collar between each rocker and the adjoining synchro ring--or pair of synchro rings on opposite sides of the first gear--prevents the exertion of a radially inwardly directed frictional force upon the synchro ring by a rocker tilted in the axial or the peripheral direction.